feat: add the disks and cache cards

disks draws a ring per filesystem from the df sample, with the NFS
server address read from the device field and a labelled-bar fallback
when the rings would be too small to read. cache shows the ~/.cache
total and its four largest children from the du sample.

card.ring now resets the cairo path first: a preceding card.text()
leaves a current point, and cairo_arc() joins to it with a straight
line, so the disks rings were drawn with stray chords. The ring
primitive had no caller until now, which is why it went unnoticed.

4 files changed, 204 insertions, 0 deletions

diff --git a/dashboard.lua b/dashboard.lua
index cbfdd68..9b527ce 100644
--- a/dashboard.lua
+++ b/dashboard.lua
@@ -24,6 +24,8 @@ local layout = {
   { widget = 'weather', col = 1, row = 6, w = 3, h = 5 },
   { widget = 'system', col = 4, row = 1, w = 3, h = 6 },
   { widget = 'gpu', col = 7, row = 1, w = 3, h = 3 },
+  { widget = 'disks', col = 7, row = 4, w = 5, h = 4 },
+  { widget = 'cache', col = 12, row = 4, w = 3, h = 4 },
 }
 -- ==========================================================================
 
diff --git a/lib/card.lua b/lib/card.lua
index 8e04e0b..48a7f2e 100644
--- a/lib/card.lua
+++ b/lib/card.lua
@@ -184,6 +184,10 @@ function M.ring(cr, cx, cy, r, frac, colour, colors, width)
   if frac < 0 then frac = 0 elseif frac > 1 then frac = 1 end
   width = width or math.max(3, r * 0.18)
 
+  -- Start a fresh path. A preceding card.text() leaves a current point behind,
+  -- and cairo_arc() joins to it with a straight line, so without this every
+  -- ring after a label is drawn with a stray chord to the text baseline.
+  cairo_new_path(cr)
   cairo_set_line_width(cr, width)
   cairo_set_line_cap(cr, CAIRO_LINE_CAP_ROUND)
 
diff --git a/widgets/cache.lua b/widgets/cache.lua
new file mode 100644
index 0000000..a1a42e3
--- /dev/null
+++ b/widgets/cache.lua
@@ -0,0 +1,63 @@
+-- Cache: ~/.cache total and its four largest subdirectories.
+--
+-- Reads a cache file written by bin/cache-sample.sh. du walks the tree and
+-- costs about 100ms, which cannot happen on a 2-second draw.
+
+local card = require 'lib.card'
+local data = require 'lib.data'
+
+local CACHE = (os.getenv('XDG_CACHE_HOME') or (os.getenv('HOME') .. '/.cache'))
+  .. '/udt/cachesize.txt'
+
+local M = {}
+
+function M.draw(cr, rect, colors)
+  local inner = card.card(cr, rect, colors)
+  local function clamp(v, lo, hi) return math.max(lo, math.min(hi, v)) end
+  local label_size = clamp(inner.w * 0.030, 10, 16)
+  local big_size   = clamp(inner.w * 0.075, 22, 46)
+
+  card.font(cr, card.FONT_MONO, label_size, false)
+  card.rgba(cr, colors.label)
+  card.text(cr, inner.x, inner.y + label_size, 'CACHE')
+
+  local c = data.du_parse(data.slurp(CACHE) or '')
+  if not c then
+    card.rgba(cr, colors.label)
+    card.font(cr, card.FONT_UI, label_size * 1.2, true)
+    card.text(cr, inner.x, inner.y + label_size * 3.4, 'no cache data')
+    card.font(cr, card.FONT_MONO, label_size, false)
+    card.text(cr, inner.x, inner.y + label_size * 5, 'bin/cache-sample.sh')
+    return
+  end
+
+  card.font(cr, card.FONT_HEAVY, big_size, false)
+  card.rgba(cr, colors.body)
+  card.text(cr, inner.x, inner.y + label_size + big_size, c.total.label)
+
+  local ey = inner.y + label_size + big_size + label_size * 2
+  local step = label_size * 2.2
+
+  card.font(cr, card.FONT_MONO, label_size, false)
+  for i, e in ipairs(c.items) do
+    if ey + step > inner.y + inner.h then break end
+    -- The biggest offender is the point of the card, so it carries colour:
+    -- critical when it is over half the total, warning otherwise. The rest
+    -- stay in the ordinary value colour so the eye lands on the one to delete.
+    local colour = colors.value
+    if i == 1 then
+      local share = c.total.bytes > 0 and (e.bytes / c.total.bytes) or 0
+      colour = share > 0.5 and colors.critical or colors.warning
+    end
+    card.rgba(cr, colors.label)
+    -- Long names are truncated rather than allowed to collide with the size.
+    local name = e.name
+    if #name > 18 then name = name:sub(1, 17) .. '\u{2026}' end
+    card.text(cr, inner.x, ey, name)
+    card.rgba(cr, colour)
+    card.text_right(cr, inner.x + inner.w, ey, e.label)
+    ey = ey + step
+  end
+end
+
+return M
diff --git a/widgets/disks.lua b/widgets/disks.lua
new file mode 100644
index 0000000..aff3e5b
--- /dev/null
+++ b/widgets/disks.lua
@@ -0,0 +1,135 @@
+-- Disks: one ring per filesystem, after idea2.png.
+--
+-- Reads a cache file written by bin/disks-sample.sh and never calls statfs
+-- itself: an unreachable NFS server blocks that call, and blocking the draw
+-- freezes the whole dashboard.
+
+local card = require 'lib.card'
+local data = require 'lib.data'
+
+local M = {}
+
+local CACHE = (os.getenv('XDG_CACHE_HOME') or (os.getenv('HOME') .. '/.cache'))
+  .. '/udt/disks.txt'
+
+-- mount -> centre glyph and the small text under it.
+--
+-- The icon IS the label: no mount name is drawn, because a Slackware S or a
+-- house says which filesystem this is faster than the word does. Every
+-- codepoint here was taken from the old conky config and re-rendered to
+-- confirm it, rather than guessed: an earlier guess at the Slackware mark
+-- (F83C) turned out to draw a stomach, and a wrong-but-present codepoint
+-- fails plausibly rather than visibly.
+--
+-- The two NFS shares are told apart by their server's address, which is read
+-- from the mount's device field at runtime rather than written here. The
+-- addresses belong on the screen, not in a public repo, and deriving them also
+-- means the card keeps working if the LAN is renumbered. It fits: at a 50px
+-- radius the usable inner width is about 75px and an address measures 58px at
+-- 10px type.
+--
+-- A mount not listed still draws, with a generic disk glyph and the last path
+-- segment, so adding one to the sampler needs no change here.
+local GLYPH = {
+  ['/']                = '\u{F318}',   -- Slackware
+  ['/home']            = '\u{F015}',   -- house
+  ['/data']            = '\u{F02CA}',  -- hard disk
+}
+local NFS_GLYPH      = '\u{F06F3}'     -- network share
+local FALLBACK_GLYPH = '\u{F02CA}'
+
+function M.draw(cr, rect, colors)
+  local inner = card.card(cr, rect, colors)
+  local function clamp(v, lo, hi) return math.max(lo, math.min(hi, v)) end
+  local label_size = clamp(inner.w * 0.030, 10, 16)
+
+  card.font(cr, card.FONT_MONO, label_size, false)
+  card.rgba(cr, colors.label)
+  card.text(cr, inner.x, inner.y + label_size, 'DISKS')
+
+  local fs = data.df_parse(data.slurp(CACHE) or '')
+  if #fs == 0 then
+    card.rgba(cr, colors.label)
+    card.font(cr, card.FONT_UI, label_size * 1.2, true)
+    card.text(cr, inner.x, inner.y + label_size * 3.4, 'no disk data')
+    card.font(cr, card.FONT_MONO, label_size, false)
+    card.text(cr, inner.x, inner.y + label_size * 5, 'bin/disks-sample.sh')
+    return
+  end
+
+  local top = inner.y + label_size * 2.2
+  local avail_h = (inner.y + inner.h) - top
+
+  -- Lay the rings out in a row, wrapping if the card is narrow. Below the
+  -- radius where a ring reads, fall back to labelled bars rather than drawing
+  -- a row of illegible dots.
+  local n = #fs
+  local per_row = n
+  local cell_w = inner.w / per_row
+  local r = math.min(cell_w * 0.34, avail_h * 0.30)
+
+  if r >= 18 then
+    for i, e in ipairs(fs) do
+      -- host is non-nil exactly for a network mount, since a local device is
+      -- a path and carries no 'server:' prefix.
+      local glyph = GLYPH[e.mount] or (e.host and NFS_GLYPH) or FALLBACK_GLYPH
+      local sub = e.host
+      if not sub and not GLYPH[e.mount] then
+        sub = (e.mount:match('([^/]+)/?$') or e.mount):upper()
+      end
+      local cx = inner.x + cell_w * (i - 0.5)
+      local cy = top + r + 6
+      local colour = card.threshold(e.pct, 25, 75, colors)
+
+      card.ring(cr, cx, cy, r, e.pct / 100, colour, colors)
+
+      -- Glyph at the centre. Drawn at 0.55 of the radius rather than 0.7: the
+      -- network-share glyph carries a wide horizontal connector that runs past
+      -- the ring at larger sizes, which reads as a line joining the rings
+      -- together.
+      local gsize = r * 0.55
+      card.font(cr, card.FONT_MONO, gsize, false)
+      card.rgba(cr, colors.label)
+      local gw = card.measure(cr, glyph)
+      -- Raised when there is text under it, centred when there is not.
+      card.text(cr, cx - gw / 2, cy + (sub and gsize * 0.10 or gsize * 0.38), glyph)
+
+      -- The address, inside the ring beneath the glyph. Only the NFS shares
+      -- have one; the local mounts are identified by their icon alone.
+      if sub then
+        card.font(cr, card.FONT_MONO, clamp(r * 0.20, 9, 12), false)
+        card.rgba(cr, colors.label)
+        local sw_ = card.measure(cr, sub)
+        card.text(cr, cx - sw_ / 2, cy + r * 0.55, sub)
+      end
+
+      -- The percentage sits under the ring, in the threshold colour.
+      card.font(cr, card.FONT_MONO, label_size, false)
+      card.rgba(cr, colour)
+      local pct = string.format('%d%%', e.pct)
+      local pw = card.measure(cr, pct)
+      card.text(cr, cx - pw / 2, cy + r + label_size * 1.7, pct)
+    end
+  else
+    local step = label_size * 2.6
+    local ey = top + label_size
+    for _, e in ipairs(fs) do
+      if ey + step > inner.y + inner.h then break end
+      -- The bar fallback has no room for a ring, so it shows the glyph inline
+      -- followed by the address or the mount name.
+      local glyph = GLYPH[e.mount] or (e.host and NFS_GLYPH) or FALLBACK_GLYPH
+      local name = e.host or (e.mount:match('([^/]+)/?$') or e.mount):upper()
+      local colour = card.threshold(e.pct, 25, 75, colors)
+      card.font(cr, card.FONT_MONO, label_size, false)
+      card.rgba(cr, colors.label)
+      card.text(cr, inner.x, ey, glyph .. '  ' .. name)
+      card.rgba(cr, colour)
+      card.text_right(cr, inner.x + inner.w, ey,
+        string.format('%s / %s', card.human(e.used), card.human(e.size)))
+      card.bar(cr, inner.x, ey + 6, inner.w, 6, e.pct / 100, colour, colors)
+      ey = ey + step
+    end
+  end
+end
+
+return M